Power management methods and systems

ABSTRACT

Power management methods and systems for a first station and a second station in an ad-hoc network. Each station enters the normal beacon interval (NBI) every certain number of beacon intervals (BIs) for data transmission, a Listen Interval (LI). When a station switches to a power-saving mode, it first determines the number of “beacon-window-only beacon intervals (BBIs)” within a LI. In addition, each station broadcasts a beacon frame comprising at least information about “the remaining number of BIs (RBI)” within a beacon window. Once the first station correctly receives the beacon frame from the second station, the first station predicts the NBI of the second station according to the RBI. At the NBI of the second station, the first station transmits data frames to the second station.

BACKGROUND OF THE INVENTION

1. Field of the Invention

The present disclosure relates generally to medium access control withpower management methods and systems, and, more particularly to methodsand systems for use in an ad hoc wireless network, where stations cantransmit data accurately when operating in the power saving mode.

2. Description of the Related Art

Currently, the IEEE 802.11 is the most popular international mediumaccess control (MAC) standard for WLANs (Wireless Local Area Networks).Based on the network architecture, wireless networks can beapproximately divided two classes: infrastructure WLANs and ad hocnetworks. FIG. 1 is a schematic diagram illustrating an ad hoc network.As shown in FIG. 1, each station (110, 120, 130, 140 and 150) candynamically communicate with adjacent stations for data transmissions.

FIG. 2 is a schematic diagram illustrating a power consumption model fora general wireless network interface card (or adapter). Each station canstay in one of the transmission, reception, listen, or doze states. Asshown in FIG. 2, the power consumption is approximately between 1.6 W to1.2 W when the station stays in either the transmission, reception, orlisten states, but is close to zero when staying in the doze state. InIEEE 802.11 power management for ad hoc networks, time is divided intofixed-sized BIs (Beacon Intervals), each of which contains an ATIM(Announcement Traffic Indication Message) window. Each station in apower saving mode (or called “power-saving station) must wake up at thebeginning of each BI and remain awake in the ATIM window, awaiting theATIM frame from other stations. If no ATIM frame is received in the ATIMwindow, then that station may enter the doze state after the ATIM windowends. If an ATIM frame is received in the ATIM window, then the stationshould reply the ATIM ACK (Acknowledgement) to the station transmittingthe ATIM frame, and remains awake after the ATIM window ends. After theend of the ATIM window, the station which sending ATIM frames should usethe DCF (distributed coordination function) procedure to transmit thebuffered data frames to its intended destination, and the destinationshould acknowledge its receipt. For a more detailed presentation, pleaserefer to IEEE 802.11 specification.

FIG. 3 is a schematic diagram illustrating an example of powermanagement in an ad hoc network based on IEEE 802.11. As shown in FIG.3, when a BI 1 begins (the timing is referred to as TBTT (Target BeaconTransmission Time)), stations X and Y compete to transmit a beacon framefor timing synchronization. It is understood that, in the example ofFIG. 3, station X transmits a beacon frame for timing synchronizationbetween stations comprising station X in the network. Since no ATIMframe is received in the ATIM window (AW for short), both stations X andY enter the doze state (S) after the AW ends. BI 2 begins, and station Xsuccessfully transmits a beacon frame. Since station X receives an ATIMframe A from station Y in the AW of BI 2, station X returns a ATIM ACK ato station Y, and remains awake after the AW ends. After the AW ends,station Y can transmit a data frame D to station X, and station Xreturns a data ACK d to station Y after receiving the data frame D.

As described, in IEEE 802.11, each station in power saving mode mustwake up in the ATIM window of “every” BI even if its battery power islow or there is no traffic for it. Hence we hope that each a powersaving station can dynamically tune its listen interval (the number ofBIs between two adjoining AWs) according to the remaining battery powerstatus or other QoS considerations. Obviously, the value of LI is fixedat “one” in IEEE 802.11. In the invention, the LI of a power savingstation can be adjusted according to parameters of quality of service orthe remaining power of the station, substantially reducing powerconsumption on station.

BRIEF SUMMARY OF THE INVENTION

Power management methods and systems are provided.

In an embodiment of a power management method for use in a first stationand a second station, three kinds of BIs comprising NBIs (Normal BeaconIntervals), BBIs (Beacon-Window-Only Beacon Intervals), and SBIs (SleepBeacon Intervals) are provided if the first and second stations stay ina power saving mode. The first and second stations enter the NBI everycertain number of BIs for data transmission, where the certain number ofBIs is LI. First, the first and second stations respectively determine anumber of BBIs within LI. Each station broadcasts a beacon framecomprising work information within a beacon window if the station staysin the BBI, in which the work information comprises a RBI (the remainingnumber of BIs) between the BBI where the beacon frame is transmitted andthe NBI. After the beacon window ends, the station enters a doze state.Once the first station correctly receives the beacon frame from thesecond station, the first station predicts the NBI of the second stationaccording to the RBI in the work information, and transmits data framesto the second station at the NBI of the second station based on the IEEE802.11.

An embodiment of a power management system comprises an ad hoc networkcomprising a first station and a second station. The first and secondstations enter a NBI every certain number of BIs for data transmission,where the certain number is LI. The first and second stationsrespectively determine a number of BBIs within the certain number ofBIs, and broadcast a beacon frame within a beacon window of the BBI, inwhich the beacon frame comprises a RBI. Once the first station correctlyreceives the beacon frame from the second station, the first stationpredicts the NBI of the second station according to the RBI in the workinformation, and transmits data frames to the second station at the NBIof the second station.

In an embodiment of a power management method for use in a first stationand a second station in an ad hoc network, in which the first and secondstations enter a NBI for data transmission every a certain number ofBIs, where the certain number is a LI value, the first and secondstations respectively determine a number of BBIs within the certainnumber of BIs, and broadcast a beacon frame within a beacon window ofthe BBI, in which the beacon frame comprises a RBI representing theremaining number of BIs between the BBI where the beacon frame istransmitted and the NBI. Once the first station correctly receives thebeacon frame from the second station, the first station predicts the NBIof the second station according to the RBI, and transmits a data frameto the second station at the NBI of the second station.

Power management methods and systems may take the form of program codeembodied in a tangible media. When the program code is loaded into andexecuted by a machine, the machine becomes an apparatus for practicingthe disclosed method.

BRIEF DESCRIPTION OF THE DRAWINGS

The invention will become more fully understood by referring to thefollowing detailed description with reference to the accompanyingdrawings, wherein:

FIG. 1 is a schematic diagram illustrating an ad hoc network;

FIG. 2 is a schematic diagram illustrating a power consumption model ofa general wireless network adapter;

FIG. 3 is a schematic diagram illustrating an example of powermanagement in an ad hoc network based on IEEE 802.11;

FIG. 4 is a schematic diagram illustrating an embodiment of a powermanagement system;

FIG. 5 is a schematic diagram illustrating an embodiment of a NBI;

FIG. 6 is a schematic diagram illustrating an embodiment of a BBI;

FIG. 7 is a schematic diagram illustrating an embodiment of a SBI;

FIG. 8 is a flowchart showing an embodiment of an initial settingmethod, for stations;

FIG. 9 is a schematic diagram illustrating an embodiment of an exampleof initial setting for a station;

FIG. 10 is a flowchart showing an embodiment of a data transmissionmethod;

FIG. 11 is a flowchart showing an embodiment of a method for beaconframe maintenance; and

FIG. 12 is a flowchart showing another embodiment of a method for beaconframe maintenance.

DETAILED DESCRIPTION OF THE INVENTION

Power management methods and systems are provided.

FIG. 4 is a schematic diagram illustrating an embodiment of a powermanagement system. As shown in FIG. 4, the power management system 400comprises an ad hoc network comprising at least a first station 410 anda second station 420. The first station 410 and the second station 420can be devices with wireless communication capability, such ascomputers, PDAs, mobile phones, and smart phones, but are not limitedthereto. The first station 410 and the second station 420 cancommunicate with each other using radio waves 430.

In the invention, the BI comprises NBIs (Normal Beacon Intervals), BBIs(Beacon-Window-Only Beacon Intervals), and SBIs (Sleep BeaconIntervals).

FIG. 5 is a schematic diagram illustrating an embodiment of a NBI. Asshown in FIG. 5, the NBI includes a AW comprising a BW (Beacon Window).It is understood that the BW must be less than the AW. Stations cantransmit data in the NBI. Specifically, stations can transmit andreceive beacon frames within the BW. Stations can transmit and receiveATIM frames within the AW except during the interval of the BW. If astation receives an ATIM frame within the AW, the station must return anATIM ACK to a station transmitting the ATIM frame. If a station receivesan ATIM frame within the AW, the station remains awake after the AW endsto await reception of data frames, and returns a data ACK if a dataframe is received. FIG. 6 is a schematic diagram illustrating anembodiment of a BBI. As shown in FIG. 6, the BBI includes a BW.Similarly, stations can transmit and receive beacon frames within theBW. Stations enter the doze state within the BBI except during theinterval of the BW. In some embodiments, no matter whether a beaconframe from other stations is received, each station must transmit itsown beacon frames to other stations in its own BWs. FIG. 7 is aschematic diagram illustrating an embodiment of a SBI. Stations enterthe doze state in the SBI.

It is understood that each station can set a LI (Listen Interval) value,and enters the NBI every certain number of BIs, where the certain numberis LI. Further, the beacon frame transmitted within the BW comprises theLI value and a RBI (the remaining number of BIs). The RBI is theremaining number of BIs within a LI, that is, the remaining number ofBIs between the BBI where the beacon frame is transmitted and the NBI.

FIG. 8 is a flowchart showing an embodiment of an initial setting methodfor stations. In step S810, the LI value is set, and in steps S820 andS830, the numbers of BBIs and SBIs within the LI are set. If the LIvalue is n, the number of BBIs in the LI is k−1, and the number of SBIsin the LI is n−k, in which k<=n. It is noted that since the first BI inthe LI is a NBI, the total number of BBIs and SBIs is the LI valueminus 1. FIG. 9 is a schematic diagram illustrating an embodiment of anexample of initial setting for a station. In the example of FIG. 9, theLI value of station X is 7, that is, station X enters a NBI every 7 BIs.Station X can transmit data in the NBI. In this example, the number ofBBIs is 3, and the number of SBIs is 3. Therefore, 4 BWs comprising theBW in the NBI are in the LI, and station X can transmit and receivebeacon frames within the BWs. It is understood that the position ofrespective BBIs and SBIs can be arbitrarily determined.

FIG. 10 is a flowchart showing an embodiment of a data transmissionmethod. It is understood that the station 420 transmits beacon frames tothe first station 410, and the first station 410 transmits data framesto the second station 420. At the same time, the first station 410 cantransmit beacon frames to the second station 420, the related details ofwhich are omitted here.

In step S1010, the second station 420 transmits beacon frames to thefirst station 410 within the BWs of the NBI and BBIs. It is understoodthat, in some embodiments, the second station 420 can transmit beaconframes to the first station 410 within at least one BW or every BWs.Each beacon frame comprises the LI value and the RBI. After the firststation 410 receives a beacon frame from the second station 420, in stepS1020, the LI value and the RBI is stored in a storage device (notshown) such as a cache. In step S1030, the first station 410 predictsthe NBI of the second station 420 according to the RBI. In step S1040,it is determined whether the NBI of the second station 420 is present.If not, the procedure remains at step S1040. If so, in step S1050, thefirst station 410 transmits an ATIM frame to the second station 420within the AW of the NBI of the second station 420. After the secondstation 420 receives the ATIM frame from the first station 410, in stepS1060, the second station 420 returns an ATIM ACK to the first station410. It is understood that if the second station 420 received the ATIMframe within the AW, the second station 420 remains awake after the AWends for awaiting reception of data frames from the first station 410.After the AW ends, in step S1070, the first station 410 transmits a dataframe to the second station 420. After the second station 420 receivesthe data frame, in step S1080, the second station 420 returns a data ACKto the first station 410.

FIG. 11 is a flowchart showing an embodiment of a method for beaconframe maintenance. In step S1110, it is determined whether a beaconframe is received from a station. If not, the procedure remains at stepS1110. If so, in step S1120, the LI value and the RBI in the beaconframe are recorded. In step S1130, it is determined whether a BI passes.If not, the procedure remains in step S1130. If so, in step S1140, theRBI is reduced by 1, and in step S1150, it is determined whether the RBIequals 0. If not, the procedure is complete. If so, in step S1160, theRBI is set as the LI value.

FIG. 12 is a flowchart showing another embodiment of a method for beaconframe maintenance. In step S1210, it is determined whether a beaconframe is received from a station. If so, in step S1220, the LI value andthe RBI corresponding to the station are updated. If not, in step S1230,it is determined whether beacon frames transmitted from the same stationare received in a predetermined interval. If the time difference betweentwo beacon frames does not exceed the predetermined interval, theprocedure returns to step S1210. If no new beacon frame corresponding tothe same station is received, in step S1240, the LI value and the RBIcorresponding to the station are deleted.

Power management methods and systems, or certain aspects or portionsthereof, may take the form of program code (i.e., executableinstructions) embodied in tangible media, such as floppy diskettes,CD-ROMS, hard drives, or any other machine-readable storage medium,wherein, when the program code is loaded into and executed by a machine,such as a computer, the machine thereby becomes an apparatus forpracticing the methods. The methods may also be embodied in the form ofprogram code transmitted over some transmission medium, such aselectrical wiring or cabling, through fiber optics, or via any otherform of transmission, wherein, when the program code is received andloaded into and executed by a machine, such as a computer, the machinebecomes an apparatus for practicing the disclosed methods. Whenimplemented on a general-purpose processor, the program code combineswith the processor to provide a unique apparatus that operatesanalogously to application specific logic circuits.

While the invention has been described by way of example and in terms ofpreferred embodiment, it is to be understood that the invention is notlimited thereto. Those who are skilled in this technology can still makevarious alterations and modifications without departing from the scopeand spirit of this invention. Therefore, the scope of the presentinvention shall be defined and protected by the following claims andtheir equivalents.

1. A power management method for use in a first station and a secondstation, in which the second station enters a NBI (Normal BeaconInterval) every certain number of BIs (Beacon Intervals) for datatransmission, where the certain number is a LI (Listen Interval) value,comprising: determining a number of BBIs (Beacon-Window-Only BeaconIntervals) within the certain number of BIs, in which the second stationbroadcasts a beacon frame within at least one of the BBI, the beaconframe comprises a RBI representing the remaining number of BIs betweenthe BBI where the beacon frame is transmitted and the NBI; and the firststation receiving the beacon frame from the second station, predictingthe NBI of the second station according to the RBI, and transmitting adata frame to the second station at the NBI of the second station. 2.The method of claim 1 further comprising: the second stationtransmitting the beacon frame comprising the LI value to the firststation; the first station reducing the RBI by 1 if one of the BIpasses; and setting the RBI as the LI value if the RBI equals
 0. 3. Themethod of claim 1 further comprising the first station deleting the RBIcorresponding to the beacon frame if no other beacon frame is receivedfrom the second station.
 4. The method of claim 1 further comprisingdetermining the number of SBIs (Sleep Beacon Intervals), in which thesecond station enters a doze state in the SBIs.
 5. The method of claim 4wherein the number of the BBIs and the SBIs equals the LI value minus 1.6. The method of claim 1 wherein each BBI comprises a BW (BeaconWindow), the second station transmits the beacon frame within the BW,and enters a doze state in the BBI except during the interval of the BW.7. The method of claim 1 wherein the NBI comprises an AW (ATIM Window)comprising a BW (Beacon Window), and the second station transmits thebeacon frame within the BW of the NBI.
 8. The method of claim 7 furthercomprising: the first station transmitting an ATIM frame to the secondstation within the AW of the NBI of the second station; the secondstation transmitting an ATIM ACK to the first station in response to theATIM frame; the first station transmitting the data frame to the secondstation within the NBI after the AW ends; and the second stationtransmitting a data ACK to the first station after receiving the dataframe.
 9. A power management system, comprising: a second stationentering a NBI (Normal Beacon Interval) every certain number of BIs(Beacon Intervals) for data transmission, where the certain number is aLI (Listen Interval) value, determining a number of BBIs(Beacon-Window-Only Beacon Intervals) within the certain number of BIs,broadcasting a beacon frame within at least one of the BBI, in which thebeacon frame comprises a RBI representing the remaining number of BIsbetween the BBI where the beacon frame is transmitted and the NBI; and afirst station receiving the beacon frame from the second station,predicting the NBI of the second station according to the RBI, andtransmitting a data frame to the second station at the NBI of the secondstation.
 10. The system of claim 9 wherein the second station furthertransmits the beacon frame comprising the LI value to the first station,the first station reduces the RBI by 1 if one of the BI passes, and setsthe RBI as the LI value if the RBI equals
 0. 11. The system of claim 9wherein the first station further deletes the RBI corresponding to thebeacon frame if no other beacon frame is received from the secondstation.
 12. The system of claim 9 wherein the second station furtherdetermines the number of SBIs (Sleep Beacon Intervals), in which thesecond station enters a doze state in the SBIs.
 13. The system of claim12 wherein the number of the BBIs and the SBIs equals the LI valueminus
 1. 14. The system of claim 9 wherein each BBI comprises a BW(Beacon Window), the second station transmits the beacon frame withinthe BW, and enters a doze state in the BBI except during the interval ofthe BW.
 15. The system of claim 9 wherein the NBI comprises an AW (ATIMWindow) comprising a BW (Beacon Window), the second station transmitsthe beacon frame within the BW of the NBI.
 16. The system of claim 15wherein the first station further transmits an ATIM frame to the secondstation within the AW of the NBI of the second station, the secondstation transmits an ATIM ACK to the first station in response to theATIM frame, the first station transmits the data frame to the secondstation within the NBI after the AW ends, and the second stationtransmits a data ACK to the first station after receiving the dataframe.
 17. A power management method for use in a second station, inwhich the second station enters a NBI (Normal Beacon Interval) everycertain number of BIs (Beacon Intervals) for data transmission, wherethe certain number is a LI (Listen Interval) value, comprising:determining a number of BBIs (Beacon-Window-Only Beacon Intervals)within the certain number of BIs, in which the second station broadcastsa beacon frame within at least one of the BBI, the beacon framecomprises a RBI representing the remaining number of BIs between the BBIwhere the beacon frame is transmitted and the NBI; and receiving a dataframe from a first station at the NBI.
 18. The method of claim 17further comprising: the first station receiving the beacon frame fromthe second station; predicting the NBI of the second station accordingto the RBI; and transmitting the data frame to the second station at theNBI of the second station.
 19. The method of claim 17 further comprisingdetermining the number of SBIs (Sleep Beacon Intervals), in which thesecond station enters a doze state in the SBIs.
 20. The method of claim19 wherein the number of the BBIs and the SBIs equals the LI valueminus
 1. 21. The method of claim 17 wherein each BBI comprises a BW(Beacon Window), the second station transmits the beacon frame withinthe BW, and enters a doze state in the BBI except during the interval ofthe BW.
 22. The method of claim 17 wherein the NBI comprises an AW (ATIMWindow) comprising a BW (Beacon Window), the second station transmitsthe beacon frame within the BW of the NBI.
 23. The method of claim 22further comprising: the first station transmitting an ATIM frame to thesecond station within the AW of the NBI of the second station; thesecond station transmitting an ATIM ACK to the first station in responseto the ATIM frame; the first station transmitting the data frame to thesecond station within the NBI after the AW ends; and the second stationtransmitting a data ACK to the first station after receiving the dataframe.